1. Field of the Invention
The present invention relates to a tubing bit opener and, in particular, to such a device adapted for the installation of caissons in earth formations.
2. Description of the Prior Art
In applicant's Canadian Patent No. 667,133, issued July 23, 1963, there is disclosed a drill employing impact cutters which in one position extend beyond the diameter of the drill body but in another position, can be retracted so that the drill can be removed through a caisson in position in the hole which has been drilled.
In applicant's Canadian Patent No. 1,216,277, issued Jan. 6, 1987 an improved device of the same type is disclosed, but which uses rotary cutters and has the advantages of easy disassembly for maintenance and repair.
The present invention relates to a further improvement to the prior devices by simplifying the construction and operation of the upper rotary cutter assembly and thereby further improving the ease of repair and maintenance.